Rhabdomyosarcoma

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Rhabdomyosarcoma

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Rhabdomyosarcomas are a malignancy of connective tissue in which abnormal cells are thought to arise from primitive muscle cells. They account for more than half of all tissue sarcomas (ie cancer of the connective tissue) in children. Other types of sarcomas are liposarcomas, fibrosarcomas and mesenchymomas.

Rhabdomyosarcomas can occur anywhere in the body but occur more commonly near muscular structures - eg, around the intestines, around the ocular muscles and in the cardiac muscle in tuberous sclerosis.[1]The most common locations of rhabdomyosarcomas are:

Head and neck (35-40%).

Bladder (20%).

Muscles, limbs, chest and abdominal wall (15-20%).

Other sites - eg, testes.

Rhabdomyosarcomas are highly malignant and grow rapidly. They are, however, potentially curable now.

Epidemiology

Rhabdomyosarcomas are rare but are the most common soft tissue sarcoma in children.[2]

Rhabdomyosarcomas is diagnosed in children and adolescents with an annual incidence of 4.3 cases per one million people younger than 20 years of age[3].

Rhabdomyosarcomas can occur at any age but approximately 87% of patients are younger than 15 years. Rhabdomyosarcoma rarely affects adults.[4]

Types

Rhabdomyosarcomas arise from rhabdomyoblasts - a primitive muscle cell. There are four types:[5]

Embryonal rhabdomyosarcoma - the cells have a similar appearance to embryo cells aged 6-8 weeks. This is the most common type and has a predilection for the head, neck and the genitourinary tract. Sarcoma botryoides is a variant of the embryonal type and presents as a grape-like lesion, particularly in the vagina or bladder.

Alveolar rhabdomyosarcoma - the cells have a similar appearance to embryo cells aged 10-12 weeks. This tends to affect older children and teenagers and has a more aggressive nature. It is associated with muscles of the trunk and limbs.

Pleomorphic rhabdomyosarcoma - this entity is more common in adults and has a tendency to affect muscles of the extremities.

Non-resolving lumps in children should be investigated by a centre recognised by the United Kingdom Children's Cancer Study Group, as they will have better expertise in these rare tumours.

Blood tests: FBC may show anaemia; LFTs may show a raised ALT and raised LDH. Urinalysis may show haematuria associated with renal tract involvement. Renal function tests and electrolytes should also be checked.

Bone marrow studies may be required (to look for infiltration).

Radiological imaging - this may include CXR and ultrasonography, and may proceed to CT or MRI scanning. More recently, positron emission tomography (PET) using radioisotope fluorodeoxyglucose (18F) (FDG-PET) scanning looks promising, especially in staging of the neoplasia.[8]

Bone scan to look for metastases.

Biopsy for diagnosis and molecular studies.

Staging

Initially, staging was identified by the Intergroup Rhabdomyosarcoma Study Group (IRSG) into the following groups:[9]

I: localised disease that is completely resected.

IIA: resected tumour with microscopic residual disease.

IIB: completely resected disease with involvement of lymph nodes.

IIC: resected tumour with microscopic residual disease (at primary site) and involvement of lymph nodes. There may also be histological involvement of the most distal regional node.

III: incomplete resection with lots of residual disease or biopsy alone of the primary site. The majority of patients belong to this group.

IV: distant metastases at the time of diagnosis.

However, the IRSG combined with another group to form the Children's Oncology Group and the above stages have been combined with the tumour, nodes, metastases (TNM) staging system to provide new stages, as follows:[9]

Disease only in favourable sites, ie the orbit, head and neck (but not parameningeal), genitourinary region (but not bladder or prostate), or biliary tract.

Disease of any other primary site (unfavorable sites). Tumours must be ≤5 cm, and no lymph node involvement.

Disease of any other primary site but >5 cm and/or lymph node involvement.

Surgical resectability without functional impairment is related to initial size and site of the tumour. Outcome is optimised with the use of multimodality therapy. All patients require chemotherapy and at least 85% also benefit from radiotherapy, with favourable outcome even for those patients with non-resectable disease.

Surgery

This is recommended for all lesions, provided it is feasible, and as much of the tumour should be removed as possible. However surgery is often not entirely successful in removing the tumour as it is often deeply embedded in surrounding tissue. If the rhabdomyosarcoma is in an extremity then amputation may be appropriate. Surgery may also be required to obtain a tissue biopsy.

Radiotherapy

Approximately 60% of all children and adolescents diagnosed with rhabdomyosarcoma are cured by currently available therapies.

However, a curative outcome is achieved in less than 30% of high-risk individuals with rhabdomyosarcoma, including all those diagnosed as adults, those diagnosed with fusion-positive tumours during childhood (including metastatic and non-metastatic tumours), and those diagnosed with metastatic disease during childhood..

The embryonal type is the most treatable and has the most favourable prognosis.

Location of the tumour also affects the prognosis, with orbital and genitourinary tract rhabdomyosarcomas having the most favourable prognosis.

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